1. Field of the Invention
The present invention relates to an optically coupled device and an optical module including the optically coupled device. In particular, the present invention relates to an optically coupled device and an optical module including the optically coupled device suitable for optically coupling a photoelectric conversion device and a multi-mode optical fiber.
2. Description of the Related Art
In recent years, with increasing speed and capacity of data communication, the need is further rising for an optical fiber communication technology using an optical fiber.
An optical fiber communication technology such as this uses an optically coupled device to which an optical fiber and a photoelectric conversion device (such as a semiconductor laser or a photodetector) are attached. In many optically coupled devices, a surface facing a photoelectric conversion element (light-emitting unit or light-receiving unit) of the photoelectric conversion device and a surface facing an end surface of the optical fiber are formed into lens surfaces.
In this type of optically coupled device, for example, light emitted from a semiconductor laser is coupled to the end surface of the optical fiber using transmittance and refraction of light by the lens surfaces.
Among optically coupled devices, some include a lens array structure in which a plurality of lens surfaces are arranged to correspond to a plurality of optical fibers (multi-core optical fiber and the like) (refer to, for example, Patent Literature 1) An optical module is configured by the photoelectric conversion device and the optical fiber being attached to an optically coupled device such as this.
Patent Literature 1: Japanese Patent Laid-open Publication No. 2005-31556
To achieve high optical coupling efficiency through appropriate optical coupling of a light-emitting unit or a light-receiving unit of the photoelectric conversion device and the end surface of the optical fiber, when the photoelectric conversion device and the optical fiber are attached to the optically coupled device, it is important that the photoelectric conversion device and the optical fiber are attached at appropriate positions on the optically coupled device.
Here, the optical fiber may be attached to the optically coupled device with a connector in a state in which an end section of the optical fiber in a longitudinal direction is held within the connector. Some connectors used in such an instance (for example, a mechanically transferable splicing connector [MT connector]) include an optical fiber-side optical fiber positioning mechanism (such as a positioning pin) for positioning the optical fiber in relation to the optically coupled device.
An optically coupled device corresponding with the optical fiber-side optical fiber positioning mechanism such as this includes an optically coupled device-side optical fiber positioning mechanism (such as a positioning hole) on the optically coupled device side that can be engaged with the optical fiber-side optical fiber positioning mechanism.
Because many optical fiber positioning mechanisms have conventionally been formed having standardized dimensions, when the optical fiber is positioned, sufficient positioning accuracy could often be achieved by merely a mechanical operation for engaging (such as by fitting) the optical fiber-side optical fiber positioning mechanism with the corresponding optically coupled device-side optical fiber positioning mechanism.
However, because a photoelectric conversion device positioning mechanism for positioning the photoelectric conversion device in relation to the optically coupled device has not been standardized, sufficient positioning accuracy is difficult to achieve by only a mechanical operation.
Therefore, conventionally, an alignment operation referred to as active alignment has been required to achieve high-accuracy positioning when the photoelectric conversion device is positioned. In active alignment, an optimal position of the photoelectric conversion device is determined through image recognition and actual emission or reception of a signal beam by the photoelectric conversion device.
When the active alignment is performed, a certain amount of error is permitted regarding alignment in the emission or irradiation direction of light in the light-emitting unit or the light-receiving unit of the photoelectric conversion device, because the error has little effect on optical coupling efficiency. However, alignment in a direction perpendicular to the emission or irradiation direction of the light in the light-emitting unit or the light-receiving unit is required to be particularly precise, because an error has a significant effect on optical coupling efficiency. A particularly precise alignment was required.
Therefore, conventionally, appropriate positioning of the photoelectric conversion device to achieve sufficient optical coupling efficiency could not be easily performed.